In my prior U.S. Pat. Nos. 2,775,077, 3,019,571 and 3,091,900 I have disclosed apparatus of the general type to which my instant invention relates. Such apparatus is accessory to centerless grinding machines or the like and comprises a floor-supported guide tube on which are arranged in spaced apart relation therealong a plurality of upwardly extending V-shaped supports with the arms of the V disposed on opposite sides of the work piece to be machined by the grinder. Booty rollers having their axes of rotation skewed to the axis of the work piece are mounted in opposed cooperating work piece supporting relation on the arms. The booty rollers are freely rotating and as the work piece is rotated in the grinder by the regulating wheel, the booty rollers support the work piece for free rotation in proper alignment with the support blade of the grinder.
It is conventional within a centerless grinder to provide a regulating wheel whose axis of rotation is adjustable relative to the axis of the work piece to be machined such that as the regulating wheel rotates in one direction it causes the work piece to rotate and at the same time translates it axially through the grinder causing the work piece to brush in grinding or polishing relation the periphery of the grinding wheel. The angular relation of the axis of the regulating wheel to the axis of the work piece is conventionally referred to as the "helix" angle of the regulating wheel. The skewed relation of the booty rollers to the axis of the work piece is intended to assist translation of the work piece through the centerless grinder.
I have found that difficulty has been encountered in satisfactorily grinding elongated work pieces following the teaching of the prior art. On occasion the work piece, particularly heavy work pieces, seem to have a tendency to stall in the grinder between the regulating wheel and the grinding wheel causing the grinder to grind a flat or dwell mark in the work piece often ruining the same. In addition, I have observed that the speed of translation of work pieces supported by prior art type work supports is not always uniform in passing through the centerless grinder and in consequence causes difficulty in reaching the desired dimension of the work piece during the grinding operation throughout the length of the work piece. In other words, as the amount of material removed from the work piece is dependent upon the exposure of the work piece to the grinding wheel, variations in the translation speed will result in variations in the amount of material removed from the work piece as it passes by the grinding wheel.
I have discovered that the aforementioned stalling as well as the variation in feed or translation rate of the work piece arises from the fact that when the operator varies the helix angle of the regulating wheel, such that the same does not correspond exactly to the skew angle of the booty rollers, the regulating wheel and booty rollers tend to "fight"; the one tending to speed up the translational movement of the work piece while the other tending to slow down the translational movement of the work piece with the result that either the regulating wheel or booty rollers will from time to time predominate in the determination of feed rate. This condition arises, in my opinion, from the fact that as an elongated work piece is being fed into the centerless grinder, a large number of booty rollers will be in supporting relation with the work piece and as the work piece enters the grinder and moves through it, fewer numbers of booty rollers will support the work piece and as a consequence, the skew angle thereof will be less predominant in determining translational rate than the helix angle of the regulating wheel. As the work piece passes through the centerless grinder and is supported by booty rollers on the outfeed side, as more and more of these rollers come in to supporting contact with the work piece the skew angle of the rollers will tend to more and more influence the translational rate of the work piece in relation to the translational rate as determined by the regulating wheel. Accordingly, varying translational rates may arise during movement of a work piece through the centerless grinder.
In severe cases the work piece may actually stall or dwell in the grinder with the concomitant result that a flat or dwell mark appears on the work piece as aforesaid. This may result from the skew angle of the booty rollers sufficiently resisting translation of the work piece so that translational movement is actually arrested in the grinder.